The molecular mechanisms of transcription by E. coli RNA polymerase and RNA polymerase II (Pol II) from the yeast S. cerevisiae. We conduct the structure/function studies of transcription elongation and investigate the mechanism of high processivity of the two closely related enzymes Escherichia coli RNA polymerase (RNAP) and RNA polymerase II (Pol II) from the yeast Saccharomyces cerevisiae. For both polymerases, we have developed a new experimental approach using synthetic DNA and RNA oligonucleotides and the solid-phase-immobilized enzymes to build in vitro authentic ternary elongation complexes (TECs) that bypass promoter-specific initiation and enzymatic synthesis of the transcript. Recently, we extended our interest toward unraveling the details of transcription through chromatin by the yeast Pol I, Pol II, and Pol III.